Entropy Change (ΔS) Calculator
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Step-by-Step Breakdown
What is Entropy Change (ΔS)?
Entropy (S) is a fundamental concept in thermodynamics that represents the degree of disorder, randomness, or energy dispersal within a system. The Entropy Change (ΔS) of a reaction measures the change in this disorder between the products and the reactants.
Calculating Reaction Entropy
Similar to enthalpy, we can calculate the standard entropy change of a reaction (ΔS°rxn) using the standard molar entropies (S°) of its components. Unlike enthalpy of formation, standard molar entropies for elements in their standard state are not zero.
The formula used is analogous to Hess's Law for enthalpy:
ΔS°rxn = Σ(m·S°)products - Σ(n·S°)reactants
A positive ΔS indicates an increase in disorder (e.g., a solid turning into a gas), while a negative ΔS indicates a decrease in disorder (e.g., gases combining to form a liquid). Entropy change is a key factor, along with enthalpy (ΔH), in determining whether a reaction will be spontaneous (using Gibbs Free Energy, ΔG = ΔH - TΔS).
Frequently Asked Questions
What are the units of entropy?
Standard molar entropy (S°) is typically measured in Joules per mole per Kelvin (J/(mol·K)). It represents the amount of disorder per mole of substance at a standard temperature (usually 298.15 K). The result of the reaction entropy change (ΔS°rxn) is therefore also usually in J/(mol·K).
What increases entropy?
Entropy generally increases when:
• Solids turn into liquids, or liquids turn into gases (phase changes to less ordered states).
• The number of moles of gas increases during a reaction.
• A solid dissolves into a solvent.
• The temperature of a substance increases.
• A complex molecule breaks down into simpler ones.
What is the Second Law of Thermodynamics?
The Second Law of Thermodynamics is a fundamental principle stating that the total entropy of an isolated system can only increase over time, or remain constant in ideal cases where the system is in a steady state or undergoing a reversible process. In simpler terms, it means that the total disorder of the universe always tends to increase. This tendency towards increased entropy is a driving force for many natural processes, including chemical reactions.
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